Optical fibers (sometimes referred to herein simply as “fibers”) are used to transmit optical signals for a variety of different applications. Optical fibers, including multimode optical fibers, are frequently used for data transmission over distances ranging from a meter or less (e.g., between telecommunication devices in a telecommunications center) up to distances of many meters (e.g., as long as several hundred meters or more), such as associated with transmitting optical signals within a local-area network either within a building or between buildings.
Multimode fibers, by definition, are designed to support multiple guided modes at a given wavelength. The bandwidth of a multimode fiber is defined by the fiber's ability to carry the different optical (guided) modes with little or no temporal separation as they travel down the fiber. This requires that the group velocities of the different optical modes be as close to the same value as possible. That is to say, there should be minimal modal dispersion (i.e., the difference in the group velocity between the different guided modes should be minimized) at a design (“peak”) wavelength λp.
Multimode fibers may be classified by the ISO 11801 standard as OM1, OM2, OM3 and OM4, based on the modal bandwidth of the multimode fiber. The OM4 fiber supports 150 meter links at 40 Gb/s and 100 Gb/s in accordance with IEE 802.3ba guidance. The letters “OM” stand for optical multimode.
Recently, there has been interest in using optical signals of different wavelengths to perform bi-directional (BiDi) optical signal transmission over a multimode fiber (MM fiber) as a cost-effective way to increase the capacity of optical fiber links for data center applications. Unfortunately, the nature of present-day MM fibers limits the range of BiDi systems to about 100 m at the data rate of 20 Gb/s due to modal dispersion that arises by using optical signals of wavelengths that are substantially different from the peak wavelength λp. Yet, there would be great benefit to extending the reach of the BiDi cabling to beyond the 100 m limit, e.g., to up to 150 m or even beyond.